Techniques for device-to-device frequency reuse in cellular networks

ABSTRACT

Device-to-device (D2D) transmissions by a wireless device may interfere with base station reception of other signals. To mitigate this interference, the wireless device estimates the path loss between itself and the base station. The path loss and the current D2D transmission power level are used to estimate the amount of interference the base station is experiencing as a result of the D2D transmissions from the wireless device. Based on the estimated interference experienced by the base station, the wireless device increases the robustness of the MCS being used and decreases the transmission power level by a corresponding amount. By decreasing the D2D transmission power level, less interference will be experienced by the base station. By increasing the robustness of the MCS, the impact of the reduced D2D transmission power level is mitigated.

This patent application is a continuation of U.S. patent applicationSer. No. 14/970,892, filed on Dec. 16, 2015, entitled TECHNIQUES FORDEVICE-TO-DEVICE FREQUENCE REUSE IN CELLULAR NETWORKS.

TECHNICAL BACKGROUND

Wireless communication networks are widely deployed to providecommunication services to both fixed and mobile devices. These servicescan include voice, data, video, messaging, web browsing, etc. Wirelesscommunication has certain advantages, such as mobility, over wiredcommunications for accessing a network. Various wireless standards havebeen adopted or proposed for wireless networks. These standards include802.11 (WiFi), 802.16 (WiMAX), TIA-856 (which is also known asEvolution-Data Optimized—EV-DO), and long term evolution (LTE).Additional standards such as the fifth generation communication system(5G) are also being pursued.

Because of transmit power regulations, limited frequency allocations,interference, and/or radio wave propagation characteristics, it isdesirable to implement the concept of device-to-device (D2D)communication for wireless devices (a.k.a., user equipment—UE.) D2Dcommunication is a peer to peer link which does not use the entirecellular network infrastructure, but enables wireless devices tocommunicate directly with one another when they are in proximity to eachother. One of the particular applications for D2D communications is foremergency services. D2D communication is also being investigated forapplications where peer discovery is required for commercialapplications in the presence of network support. Another use for D2Dcommunication is to improve user data speed, and extend cellularcoverage. However, wireless devices that are engaged in D2Dcommunication can cause interference to other devices and/or basestations.

OVERVIEW

In an embodiment, a method of operating a communication system includesreceiving, by a first wireless device, a first indicator correspondingto an access node transmission power. The first wireless device measuresa second indicator corresponding to a received signal power from theaccess node. Based on the first indictor and the second indicator, anestimated signal strength of a transmission from the first wirelessdevice arriving at the access node is calculated. Based on the estimatedsignal strength, a modulation and coding rate (MCS) for use by the firstwireless device to transmit directly to a second wireless deviceselected.

In an embodiment, a method of operating a communication system, includesconfiguring a first wireless device to communicate directly with asecond wireless device. Uplink air-interface resources are scheduledamong a plurality of wireless devices. The first wireless devicereceives a plurality of indicators of scheduled uplink air-interfaceresource. The pluralities of indicators are used to determine, by thefirst wireless device, at least one unscheduled uplink air-interfaceresource. The first wireless device communicates directly with thesecond wireless device using the at least one unscheduled uplinkair-interface resource.

In an embodiment, a communication system comprises an access node tosend indicators of scheduled uplink air-interface resources to aplurality of wireless devices. The plurality of wireless devicesincludes a first wireless device and a second wireless device. The firstwireless device is configured to receive the indicators of scheduleduplink air-interface resources. Using these indicators, the firstwireless device determines at least one unscheduled uplink air-interfaceresource that can be used by the first wireless device fordevice-to-device communication between the first wireless device and thesecond wireless device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a communication system.

FIG. 2 is a flowchart illustrating a method of selecting a modulationand coding scheme for device-to-device communication.

FIG. 3 is a flowchart illustrating a method of using unscheduledair-interface resources for device-to-device communication.

FIG. 4 is diagram illustrating guard period resources usable fordevice-to-device communication.

FIG. 5 is a diagram illustrating guard band resources usable fordevice-to-device communication.

FIG. 6 is a diagram illustrating reference signal resources usable fordevice-to-device communication.

FIG. 7 illustrates a processing node.

DETAILED DESCRIPTION

In an embodiment, device-to-device (D2D) transmissions by a wirelessdevice may interfere with base station reception of other signals. Tomitigate this interference, the wireless device estimates the path lossbetween itself and the base station. This estimate is based on thetransmission power of the base station and the signal strength of thebase station's signal as measured by the wireless device. The path lossand the current D2D transmission power level are used to estimate theamount of interference the base station is experiencing as a result ofthe D2D transmissions from the wireless device. Based on the estimatedinterference experienced by the base station, the wireless deviceincreases the robustness of the MCS being used and decreases thetransmission power level by a corresponding amount. By decreasing theD2D transmission power level, less interference will be experienced bythe base station. By increasing the robustness of the MCS, the impact ofthe reduced D2D transmission power level is mitigated.

In an embodiment, a wireless device monitors which uplink air-interfaceresources in a frame have been scheduled by the base station for use bywireless devices. The remaining air-interface resources are thereforeunscheduled and unused for communication with the base station. Thewireless device can use some (or all) of these unused (i.e.,unscheduled) uplink air-interface resources for D2D communication.

In an embodiment, wireless systems using time division duplexing mayspecify frames that have a guard period between uplink subframes anddownlink subframes. This guard period is used for time synchronizationbetween the base station and a wireless device. In an embodiment, awireless device can use some (or all) of the guard periods for D2Dcommunication.

In an embodiment, wireless systems using frequency division duplexingmay specify a channel (i.e., frequency band) that is divided into many(e.g., 2048) Orthogonal Frequency Division Multiplexing (OFDM)subcarriers. To limit out-of-band emissions that may interfere with anadjacent channel, some of these subcarriers, particularly at the edgesof a channel's frequency range, are designated as guard bands and arenot used for communication with the base station. In an embodiment, awireless device can use some (or all) of these guard subcarriers for D2Dcommunication.

In an embodiment, a base station may broadcast which air-interfaceresources (i.e., time slots or subcarriers) will not be used for‘regular’ base station communication with wireless devices over asubsequent period of time (e.g., number of frames.) This information maybe broadcast using system information transmissions (e.g., systeminformation blocks.) The wireless device can use some (or all) of thesedesignated (i.e., unscheduled) uplink air-interface resources for D2Dcommunication.

In an embodiment, some air-interface resources are designated to carrypilot signals (e.g., LTE sounding reference signals or demodulationreference signals) to aid in communication (e.g., for channelestimation, etc.) A wireless device may multiplex a prearranged (e.g.,with the other D2D device) orthogonal code onto these pilot signals touse them to carry D2D communication.

FIG. 1 is a block diagram illustrating a communication system. In FIG.1, communication system 100 comprises access node 110, wireless device131, and wireless device 132. A wireless device 131-132 each may also bereferred to as user equipment, or UE. Access node 110 is illustrated ashaving coverage area 111. Wireless device 131, and wireless device 132are located within coverage area 111.

Access node 110 is illustrated as being operatively coupled to wirelessdevice 131 via wireless link 141. Access node 110 is illustrated asbeing operatively coupled to wireless device 132 via wireless link 142.Wireless device 131 and wireless device 132 are also illustrated asbeing operatively coupled to each other via wireless link 143. Thus,wireless device 131 and wireless device 132 are configured fordevice-to-device (D2D) communication via wireless link 143. Wirelesslink 143 uses the same frequency band as wireless links 141-142. Thus,wireless device 131 and wireless device 132 are configured to use inbandD2D communication.

Access node 110 is a network node capable of providing wirelesscommunication to wireless device 131, and/or wireless device 132. Accessnode 110 can be, for example, one or more of a base transceiver station,a radio base station, an eNodeB device, or an enhanced eNodeB device.

Communication system 100 is a communication network that can providewireless communication to wireless device 131, and/or wireless device132. Communication system 100 can comprise wired and/or wirelesscommunication networks that include processing nodes, routers, gateways,physical and/or wireless data links for carrying data among variousnetwork elements, including combinations thereof, and can include alocal area network, a wide area network, and an internetwork (includingthe Internet). Communication system 100 can also comprise wirelessnetworks, including base station, wireless communication nodes,telephony switches, internet routers, network gateways, computersystems, communication links, or some other type of communicationequipment, and combinations thereof.

Wired network protocols that may be utilized by communication system 100may comprise Ethernet, Fast Ethernet, Gigabit Ethernet, Local Talk (suchas Carrier Sense Multiple Access with Collision Avoidance), Token Ring,Fiber Distributed Data Interface (FDDI), and Asynchronous Transfer Mode(ATM). Wireless network protocols that may be utilized by communicationsystem 100 may comprise code division multiple access (CDMA) 1×RTT,Global System for Mobile communications (GSM), Universal MobileTelecommunications System (UMTS), High-Speed Packet Access (HSPA),Evolution Data Optimized (EV-DO), EV-DO rev. A, Third GenerationPartnership Project Long Term Evolution (3GPP LTE), and WorldwideInteroperability for Microwave Access (WiMAX).

Links between elements of communication system 100, can be, for example,twisted pair cable, coaxial cable or fiber optic cable, or combinationsthereof. Wireless link 141, wireless link 142, and/or wireless link 143can be a radio frequency, microwave, or other similar signal. Wirelesslink 141, wireless link 142, and/or wireless link 143 can use a suitablecommunication protocol, for example, Global System for Mobiletelecommunications (GSM), Code Division Multiple Access (CDMA),Worldwide Interoperability for Microwave Access (WiMAX), or Long TermEvolution (LTE), or combinations thereof. Other wireless protocols canalso be used.

Other network elements may be present in communication system 100 tofacilitate wireless communication to/from access node 110, wirelessdevice 131 and/or wireless device 132, but are omitted for clarity, suchas base stations, base station controllers, gateways, mobile switchingcenters, dispatch application processors, and location registers such asa home location register or visitor location register. Furthermore,other network elements may be present to facilitate communicationbetween among elements of communication system 100 which are omitted forclarity, including additional processing nodes, routers, gateways, andphysical and/or wireless data links for carrying data among the variousnetwork elements.

Wireless device 131, and/or wireless device 132 may be any device,system, combination of devices, or other such communication platformcapable of communicating wirelessly with access node 110, and with eachother using D2D wireless link 143. Wireless device 131 and/or wirelessdevice 132 may be, for example, a mobile phone, a wireless phone, awireless modem, a personal digital assistant (PDA), a voice overinternet protocol (VoIP) phone, a voice over packet (VOP) phone, or asoft phone, as well as other types of devices or systems that canexchange audio or data via access node 110, and can also communicatedirectly with each other (i.e., capable of D2D communication.) Othertypes of communication platforms are possible.

In an embodiment, the device-to-device (D2D) transmissions betweenwireless device 131 and wireless device 132 via wireless link 143 mayinterfere with the reception of other signals by access node 110 (e.g.,reception of signals via wireless link 141 and/or wireless link 142). Tomitigate this interference, wireless device 131 estimates the path lossbetween itself and the base station. This estimate is based on thetransmission power of access node 110 and the signal strength oftransmissions from access node 110 as measured by wireless device 131.The path loss estimate and the current D2D transmission power level usedby wireless device 131 are used to estimate the amount of interferenceaccess node 110 is experiencing as a result of the D2D transmissionsfrom wireless device 131. Based on the estimated interferenceexperienced by access node 110, wireless device 131 can increase therobustness of the MCS being used for D2D transmissions and decrease D2Dpower level by a corresponding amount. By decreasing the D2Dtransmission power level, less interference will be experienced byaccess node 110. By increasing the robustness of the MCS, the impact ofthe reduced D2D transmission power on D2D communication via wirelesslink 143 level is mitigated.

Wireless device 131 receives a first indicator that corresponds to thetransmission power being used by access node 110. This first indicatormay be broadcast by access node 110 in, for example, a systeminformation block (SIB). Wireless device 131 measures a second indicatorthat corresponds to the signal power of transmissions from access node110 as received by wireless device 131.

Based on these two indicators, wireless device 131 calculates anestimated signal strength corresponding to the signal power of D2Dtransmissions from wireless device 131 as received by access node 110.This estimate may rely on the principle of channel reciprocity.

Wireless device 131 estimates the path loss (PL_(est)) as the differencebetween the broadcast transmission power of access node 110, and thereceived signal strength of known strength transmissions from accessnode 110, as measured by wireless device 131. Wireless device 131 mayestimate the path loss (PL_(est)) as the difference between thetransmission power of reference signals sent by access node 110(ReferenceSignalPower), and the signal strength (RSRP) of thesereference signals as measured by wireless device 131. In other words, toestimate (or calculate) the path loss:PL_(est)=ReferenceSignalPower−RSRP.

Wireless device 131 estimates the signal power of D2D transmissions bywireless device 131 arriving at access node 110. Wireless device 131estimates the signal power of D2D transmissions by wireless device 131arriving at access node 110 (P_val) by subtracting the D2D transmissionpower (PWR_(D2D)) being used by wireless device 131 to communicate withwireless device 132 from the estimated path loss (PL_(est)). In otherwords, to estimate the signal power of D2D transmissions by wirelessdevice 131 arriving at access node 110: P_val=PWR_(D2D)−PL_(est).

Wireless device 131 also estimates the baseline interference level ataccess node 110. This estimate can be based on the cellular channelbandwidth, and a noise figure associated with access node 110. In otherwords, to estimate the interference level (BS noise level) at accessnode 110: BS_noise_level(dBm)=−174 dBm/Hz+BS_noise_figure+10*log(channelbandwidth).

Wireless device 131 also estimates the interference level rise (IOT)over the baseline interference level (BS_noise_level) experienced byaccess node 110. In other words, to estimate the interference level rise(IOT) experienced at access node 110 as a result of the D2Dtransmissions by wireless device 131: IOT(dBm)=P_val−BS_noise_level.

If the interference level rise (IOT) is negative (i.e., the D2Dtransmissions by wireless device 131 do not exceed the baselineinterference level associated with access node 110), then wirelessdevice 131 does not adjust the D2D transmission power level or the D2DMCS. If the interference level rise (IOT) is positive (i.e., theestimated signal strength of D2D transmissions arriving at access node110 meets a threshold criteria), then wireless device 131 reduces thepower of, and also increases the redundancy of, the D2D transmissionsmade by wireless device 131. This reduction of transmission power andcorresponding increase in MCS can be selected according to Table 1.

TABLE 1 MCS Req'd SNR for MCS Level 0  0 dB Level 1  5 dB Level 2 10 dBLevel 3 15 dB

For example, if the current MCS for D2D transmissions from wirelessdevice 131 is level 3, and the required power reduction is 5 dB in orderto reduce the interference experienced by access node 110 as a result ofthe D2D transmissions from wireless device 131 to below the baselineinterference level (i.e., BS_noise_level), wireless device 131 willreduce, by at least 5 dB, the D2D transmission power level, and alsochange the MCS from level 3 to level 2. In another example, if thecurrent MCS is level 3, and a 7 dB power reduction is needed to reducethe D2D transmissions (as measured at access node 110) to below thebaseline interference level, wireless device 131 will reduce, by atleast 7 dB, the D2D transmission power level, and also change the MCSfrom level 3 to level 1. In another example, if the current MCS is level3, and an 11 dB D2D transmission power reduction is needed, wirelessdevice 131 will reduce, by at least 11 dB, the D2D transmission powerlevel, and also change the MCS from level 3 to level 0.

In an embodiment, wireless device 131 and wireless device 132 monitorwhich uplink air-interface resources (e.g., slots) in a frame have beenscheduled by access node 110 for use by wireless devices 131-132 (and/orother wireless devices not shown in FIG. 1) to transmit to access node110. The remaining uplink air-interface resources are thereforeunscheduled and unused for transmissions to access node 110. Wirelessdevice 131 and wireless device 132 can use some (or all) of these unused(i.e., unscheduled) uplink air-interface resources for D2Dcommunication.

Wireless device 131 and wireless device 132 are configured tocommunicate directly with each other via wireless link 143. Access node110 is configured to schedule uplink air-interface resources among thewireless devices that access node 110 is servicing. At least wirelessdevice 131 receives indicators of the scheduled uplink air-interfaceresources from access node 131. These indicators may be sent by accessnode 110 in response to requests for uplink air-interface resources madeby the wireless devices that access node 110 is servicing.

By examining these indicators, wireless device 131 can determine which(if any) uplink air-interface resources are unscheduled and thereforeare (at the corresponding time and/or frequency) going to be unused.Wireless device 131 uses at least one of these unscheduled air-interfaceresources (e.g., an unscheduled time and frequency slot) to transmitdirectly to wireless device 132.

In an embodiment, access node 110 may be configured to use time divisionduplexing on wireless links 141-142. The time division duplexing (TDD)used by access node 110 may specify frames that have a guard periodbetween uplink subframes and downlink subframes. This guard period maybe used for time synchronization between access node 110 and a wirelessdevice 131-132. Wireless device 131 uses some (or all) of a guard periodfor D2D transmissions over wireless link 143.

In an embodiment, access node 110 may be configured to use frequencydivision duplexing (FDD) on wireless links 141-142. The FDD used byaccess node 110 may specify a channel (i.e., frequency band) that isdivided into many (e.g., 2048) Orthogonal Frequency DivisionMultiplexing (OFDM) subcarriers. To limit out-of-band emissions that mayinterfere with an adjacent channel, some of these subcarriers,particularly at the edges of a channel's frequency range, are designatedas guard bands and are not used for communication with access node 110.In an embodiment, wireless device 131 an uses some (or all) of theseguard subcarriers for D2D transmissions over wireless link 143.

In an embodiment, access node 110 may broadcast which air-interfaceresources (i.e., time slots or subcarriers) will not be used for non-D2Dcommunication from wireless devices over a subsequent period of time(e.g., number of frames—also broadcast by access node 110). Theinformation that specifies which air-interface resource are to beunscheduled (and therefore unused for communication with access node110) may be broadcast by access node 110 using system informationtransmissions (e.g., system information blocks). Wireless device 131 canuse some (or all) of these designated uplink air-interface resources forD2D transmissions over wireless link 143.

In an embodiment, access node 110 is configured to use someair-interface resources to carry pilot signals (e.g., LTE soundingreference signals or demodulation reference signals) to aid incommunication (e.g., for channel estimation, etc.) Wireless device 131multiplexes a prearranged (e.g., with wireless device 132) an orthogonalcode onto these pilot signals. This allows wireless device 131 andwireless device 132 to use these air-interface resource to carry D2Dcommunication.

FIG. 2 is a flowchart illustrating a method of selecting a modulationand coding scheme for device-to-device communication. The stepsillustrated in FIG. 2 may be performed by one or more elements ofcommunication system 100. By a first wireless device, a first indicatorcorresponding to and access node transmission power is received (202).For example, Wireless device 131 may receive a first indicator thatcorresponds to the transmission power being used by access node 110.This first indicator may be broadcast by access node 110.

By the first wireless device, a second indicator corresponding to areceived signal power from the access node is measured (204).

Wireless device 131 measures a second indicator that corresponds to thesignal power of transmissions from access node 110 as received bywireless device 131. For example, wireless device 131 may measure asecond indicator that corresponds to the signal power of transmissionsfrom access node 110 as received by wireless device 131.

Based on the first indicator and the second indicator, an estimatedsignal strength of a transmission from the first wireless devicearriving at the access node is calculated (206). For example, wirelessdevice 131 may calculate an estimated signal strength corresponding tothe signal power of D2D transmissions from wireless device 131, asreceived by access node 110.

Based on the estimated signal strength, a modulation and coding schemefor use by the first wireless device to transmit directly to the secondwireless device is selected (208). For example, if the estimated signalstrength of D2D transmissions from wireless device 131 exceed thebaseline interference level associated with access node 110 (i.e., meeta threshold criteria), then wireless device 131 may reduce the power of,and also increases the redundancy of (by a corresponding amount), theD2D transmissions made by wireless device 131.

FIG. 3 is a flowchart illustrating a method using unscheduledair-interface resources for device-to-device communication. The stepsillustrated in FIG. 3 may be performed by one or more elements ofcommunication system 100. A first wireless device is configured tocommunicate directly with a second wireless device (302). For example,wireless device 131 may be configured to communicate directly withwireless device 132 via wireless link 143.

Air-interface resources are scheduled among a plurality of wirelessdevices (304). For example, access node 110 may schedule uplinkair-interface resources to be used by wireless devices 131-132 totransmit to access node 110. Access node 110 may transmit (e.g., towireless device 131 and wireless device 132) indicators that reflect thescheduling of these uplink air-interface resources (and their assignmentto a respective wireless device 131-132.)

By the first wireless device, a plurality of indicators of scheduleduplink air-interface resources are received (306). For example, wirelessdevice 131 may receive, from access node 110, a plurality of indicatorsthat correspond to which of the scheduled uplink air-interface resourceshave been scheduled (and are therefore going to be used.)

The plurality of indicator are used to determine, by the first wirelessdevice, at least one unscheduled uplink air-interface resource (308).For example, wireless device 131 can determine, from the plurality ofindicators that correspond to which of the scheduled uplinkair-interface resources have been scheduled, which uplink air-interfaceresources have not been scheduled (and are therefore are not going to beused.)

By the first wireless device, the second wireless device is communicatedwith using the at least one unscheduled uplink air-interface resource(310). For example, wireless device 131 can use some (or all) of theunused (i.e., unscheduled) uplink air-interface resources determined inblock 308 for D2D communication.

FIG. 4 is diagram illustrating guard period resources usable fordevice-to-device communication. The air-interface resource format, andguard period resources in particular, illustrated in FIG. 4 may be usedby one or more elements of communication system 100. In FIG. 4, a TDDframe 400 is illustrated. TDD frame 400 comprises ten (10) subframesSF0-SF9 that are contiguous in time. Subframe SF1 includes downlinkpilot timeslot (dwPTS) 412, guard period 414, and uplink pilot timeslot416 (upPTS). Subframe SF6 may optionally (depending upon aconfiguration) include downlink pilot timeslot 462, guard period 464,and uplink pilot timeslot 466. In an embodiment, guard period 414 andguard period 464 are not used for transmissions by an access node (e.g.,access node 110), or by wireless devices (e.g., wireless devices131-132) to transmit to the access node. In an embodiment, wirelessdevice 131 and/or wireless device 132 may transmit during guard period414 and/or guard period 464 for D2D transmissions via wireless link 143.

FIG. 5 is a diagram illustrating guard band resources usable fordevice-to-device communication. The OFDM subcarrier allocation, andguard band resources in particular, illustrated in FIG. 5 may be used byone or more elements of communication system 100. To limit out-of-bandemissions that may interfere with an adjacent channel, guard subcarriers502-503, are designated as guard bands and are not used forcommunication with an access node. In an embodiment, wireless device 131and/or wireless device 132 may transmit using guard subcarriers 502-503for D2D transmissions via wireless link 143. For example, guardsubcarriers 502 may be used by wireless device 131 for D2D transmissionsto wireless device 132. Guard subcarriers 503 may be used by wirelessdevice 132 for D2D transmissions to wireless device 131.

FIG. 6 is a diagram illustrating reference signal resources usable fordevice-to-device communication. In FIG. 6, communication system 600includes access node 610, wireless device 611, wireless device 612,wireless device 613, wireless device 614, and wireless devices 615.

Wireless device 611 transmits subframe 631 directly to wireless device612. Wireless device 613 transmits subframe 641 to wireless device 614.Access node 610 transmits subframe 651 to wireless devices 615.

Subframe 631 includes reference signal resource elements 632. Subframe641 includes reference signal resource elements 642. Subframe 651includes reference signal resource elements 652. In an embodiment, atleast some of the reference signal resource elements in subframe 631overlap, in time and frequency, reference signal resource elements insubframes 641 and 651. This is illustrated in FIG. 6 by arrows 661-664.

In an embodiment, an orthogonal code of a family of orthogonal codes ismultiplexed, by wireless device 611, onto reference signal resourceelements 632 of subframe 631. Likewise, the orthogonal code ismultiplexed onto reference signal resource elements 642 of subframe 641.Because the orthogonal code is orthogonal to the signals transmitted byaccess node 610 in reference signal resource elements 652, theinterference between reference signal resource elements 632 andreference signal resource elements 651 is mitigated. This allows theorthogonally coded (and information bearing) reference signal resourceelements 632 and 642 to be used for D2D transmissions between wirelessdevices 611-614.

The methods, systems, devices, networks, access nodes, processing node,control nodes, and equipment described above may be implemented with,contain, or be executed by one or more computer systems and/orprocessing nodes. The methods described above may also be stored on anon-transitory computer readable medium. Many of the elements ofcommunication system 300, and/or communication system 600 may be,comprise, or include computers systems and/or processing nodes. Thisincludes, but is not limited to: access node 110, wireless device 131,wireless device 132, access node 610, wireless device 611, wirelessdevice 612, wireless device 613, wireless device 614, and/or wirelessdevices 615.

FIG. 7 illustrates an exemplary processing node 700 comprisingcommunication interface 702, user interface 704, and processing system706 in communication with communication interface 702 and user interface704. Processing node 700 is capable of paging a wireless device.Processing system 706 includes storage 708, which can comprise a diskdrive, flash drive, memory circuitry, or other memory device. Storage708 can store software 710 which is used in the operation of theprocessing node 700. Storage 708 may include a disk drive, flash drive,data storage circuitry, or some other memory apparatus. Software 710 mayinclude computer programs, firmware, or some other form ofmachine-readable instructions, including an operating system, utilities,drivers, network interfaces, applications, or some other type ofsoftware. Processing system 706 may include a microprocessor and othercircuitry to retrieve and execute software 710 from storage 708.Processing node 700 may further include other components such as a powermanagement unit, a control interface unit, etc., which are omitted forclarity. Communication interface 702 permits processing node 700 tocommunicate with other network elements. User interface 704 permits theconfiguration and control of the operation of processing node 700.

An example of processing node 700 includes wireless device 131.Processing node 700 can also be an adjunct or component of a networkelement, such as an element of access node 110, access node 610, amobility management entity, a gateway, a proxy node, or another networkelement in a communication system.

The exemplary systems and methods described herein can be performedunder the control of a processing system executing computer-readablecodes embodied on a computer-readable recording medium or communicationsignals transmitted through a transitory medium. The computer-readablerecording medium is any data storage device that can store data readableby a processing system, and includes both volatile and nonvolatilemedia, removable and non-removable media, and contemplates mediareadable by a database, a computer, and various other network devices.

Examples of the computer-readable recording medium include, but are notlimited to, read-only memory (ROM), random-access memory (RAM), erasableelectrically programmable ROM (EEPROM), flash memory or other memorytechnology, holographic media or other optical disc storage, magneticstorage including magnetic tape and magnetic disk, and solid statestorage devices. The computer-readable recording medium can also bedistributed over network-coupled computer systems so that thecomputer-readable code is stored and executed in a distributed fashion.The communication signals transmitted through a transitory medium mayinclude, for example, modulated signals transmitted through wired orwireless transmission paths.

The above description and associated figures teach the best mode of theinvention. The following claims specify the scope of the invention. Notethat some aspects of the best mode may not fall within the scope of theinvention as specified by the claims. Those skilled in the art willappreciate that the features described above can be combined in variousways to form multiple variations of the invention. As a result, theinvention is not limited to the specific embodiments described above,but only by the following claims and their equivalents.

What is claimed is:
 1. A method of operating a communication system,comprising: configuring a first wireless device to communicate directlywith a second wireless device; scheduling uplink air-interface resourcesamong a plurality of wireless devices; receiving, by the first wirelessdevice, a plurality of indicators of scheduled uplink air-interfaceresources; using the plurality of indicators, determining, by the firstwireless device, at least one unscheduled uplink air-interface resource;and, communicating, by the first wireless device, directly with thesecond wireless device using the at least one unscheduled uplinkair-interface resource for device-to-device communication to transmitdata between the first and second wireless device, wherein the at leastone unscheduled uplink air-interface resource comprises a guard resourcecomprising one or both of a guard period and a guard band for thedevice-to-device communication, the data transmitted between the firstand second wireless devices via the guard resource.
 2. The method ofclaim 1, further comprising: transmitting the plurality of indicators ofscheduled uplink air-interface resources to the plurality of wirelessdevices.
 3. The method of claim 2, wherein the plurality of indicatorscorresponds to responses to uplink air-interface resource requests. 4.The method of claim 3, wherein: the uplink air-interface resourcerequests are made by the plurality of wireless devices; and theplurality of wireless devices comprises the first wireless device andthe second wireless device.
 5. The method of claim 1, wherein: thecommunication system comprises a frequency-division duplex communicationsystem; the at least one unscheduled uplink air-interface resourcecomprises unscheduled uplink channel resources in the frequency-divisionduplex communication system; and the guard resource comprises a gapband.
 6. The method of claim 1, wherein: the communication systemcomprises a time-division duplex communication system; the at least oneunscheduled uplink air-interface resource comprises to unscheduleduplink time-frame resources in the time-division duplex communicationsystem; and the guard resource comprises a gap period.
 7. The method ofclaim 1, wherein the communication system comprises a frequency divisionduplexing communication system and the guard resource comprises theguard band.
 8. The method of claim 7, wherein the uplink air-interfaceresources comprise orthogonal frequency division multiplexing (OFDM)subcarriers and the guard band comprises guard subcarriers.
 9. Themethod of claim 7, wherein the uplink air-interface resources comprise afrequency band and the guard band comprises guard subcarriers located atedges of the frequency band.
 10. The method of claim 1, wherein thecommunication system comprises a time division duplexing communicationsystem and the guard resource comprises the guard period, wherein theguard period is between uplink subframes and downlink subframes.
 11. Themethod of claim 1, wherein the at least one unscheduled uplinkair-interface resource further comprises pilot signals and the methodfurther comprises multiplexing, by the first wireless device, anorthogonal code on the pilot signals to communicate directly with thesecond wireless device.
 12. The method of claim 1, further comprisingestimating, by the first wireless device, an interference level at anaccess node caused by device-to-device transmissions from the firstwireless device to the second wireless device, wherein the plurality ofindicators of scheduled uplink air-interface resources is received fromthe access node.
 13. The method of claim 12, further comprisingselecting, by the first wireless device, a device-to-device transmissionpower level for transmissions to the second wireless device based on theestimate of the interference level at the access node caused by thedevice-to-device transmissions from the first wireless device to thesecond wireless device.
 14. The method of claim 12, further comprisingselecting, by the first wireless device, a device-to-device modulationand coding scheme (MCS) for transmissions to the second wireless devicebased on the estimate of the interference level at the access nodecaused by the device-to-device transmissions from the first wirelessdevice to the second wireless device.
 15. A communication system,comprising: an access node to send indicators of scheduled uplinkair-interface resources to a plurality of wireless devices; and, a firstwireless device configured to receive the indicators of scheduled uplinkair-interface resources and determine at least one unscheduled uplinkair-interface resource that can be used by the first wireless device fordevice-to-device communication to transmit data between the firstwireless device and a second wireless device, the plurality of wirelessdevices comprising the first wireless device and comprising the secondwireless device, wherein the at least one unscheduled uplinkair-interface resource comprises a guard resource comprising one or bothof a guard period and a guard band for the device-to-devicecommunication, the data transmitted between the first and secondwireless devices via the guard resource.
 16. The communication system ofclaim 15, wherein the first wireless device is further configured toestimate an interference level at the access node caused bydevice-to-device transmissions from the first wireless device to thesecond wireless device.
 17. The communication system of claim 16,wherein the first wireless device is further configured to select adevice-to-device transmission power level for transmissions to thesecond wireless device based on the estimate of the interference levelat the access node caused by the device-to-device transmissions from thefirst wireless device to the second wireless device.
 18. Thecommunication system of claim 16, wherein the first wireless device isfurther configured to select a device-to-device modulation and codingscheme (MCS) for transmissions to the second wireless device based onthe estimate of the interference level at the access node caused by thedevice-to-device transmissions from the first wireless device to thesecond wireless device.
 19. The communication system of claim 16,wherein the first wireless device is further configured to, based on theestimate of the interference level at the access node caused by thedevice-to-device transmissions from the first wireless device to thesecond wireless device, select a device-to-device transmission powerlevel and a device-to-device modulation and coding scheme (MCS) fortransmissions to the second wireless device.
 20. The communicationsystem of claim 19, wherein the first wireless device is furtherconfigured to, based on an indicator corresponding to a transmissionpower being used by the access node, select the device-to-devicetransmission power level and the device-to-device modulation and codingscheme (MCS).